While it is well known that electronic parts such as LSIs and IC chips generate heat during operation and concomitantly degrade their performance, a variety of heat dissipating techniques are used to solve the problem. In one common technique, heat dissipation is carried out by disposing a cooling member near a heat generating member, bringing them in close contact, and effectively removing heat from the cooling member. If a gap is left between the heat generating member and the cooling member, the heat transfer becomes inefficient due to the intervention of air having low heat conduction, failing to fully reduce the temperature of the heat generating member. For the purpose of preventing air intervention to avoid such a phenomenon, heat dissipating materials, sheets and greases having a high thermal conductivity and conformable to the member surface are employed (JP 2938428, JP 2938429 and JP 3952184: Patent Documents 1 to 3).
Of the heat dissipating greases, one exemplary grease is used in such a way that it is sandwiched between a semiconductor chip and a heat spreader and heat cured so as to bring the semiconductor chip and the heat spreader in close contact. Many such materials have been reported (JP 5047505: Patent Document 4). The hitherto known materials, however, have a high storage modulus G′. They fail to conform to warp induced between a heat generating member and a cooling member by thermal cycling caused by switching on and off of the heat generating member, suggesting a situation that the heat dissipating grease may eventually peel from the substrate. On the other hand, on use of a non-reactive grease as the material having a low storage modulus G′, pump-out may occur. Upon occurrence of peeling or pump-out as mentioned above, the close contact between the heat generating member and the cooling member is exacerbated to reduce the cooling efficiency, whereby the performance of the electronic part is degraded. The conventional materials have the problem that when peeling from the substrate or breakage of material itself occurs by warpage of a chip or heat spreader on which they are mounted, air will intervene therebetween to invite an outstanding increase of thermal resistance.